What type of battery would be best as an external power source for a device needing 12V - .80mA?

Question

tried using a 12 volt battery running @ 1.3A with a small capacitor it worked for a while but still burnt out.

Answer 1

i'm not sure what the capacitor is there for. If your device has a resistance, it will charge and discharge with the RC time constant.

your device has some resistance, apply some voltage, and the required current is V/R. if the battery is running out, you need a bigger 12V battery. Amp-hours gives you some idea of what amperage and for how long it can run

Answer 2

If you need only 80mA, 0.08 amps, then any 12 volt battery will work, this is a light load.

Where did the 1.3 amps come from, if the load is only 80mA? What is the cap for? and what burned out?